INTRODUCTION

Ventilation is a basic part of all underground mine operations. Ventilation is undertaken in order to introduce fresh, cool air to the workings and to remove stale, affected air from the workings. In this technology review, we look at the basics of ventilation, the regulations, and the people, companies, and equipment you may need for installing, operating, and maintaining a ventilation system at your mine.

The need for ventilation in an underground mine is described thus by Hardcastle, Kocsis, and Lacroix in a paper from the CIM 2007 conference, entitled Strategic mine ventilation control: A source of potential energy savings.

Ventilation in underground mines is required to dilute and remove hazardous substances, control the thermal environment, and provide oxygen for humans and engine combustion. In Canadian mines, the most common considerations are the control of diesel engine exhaust emissions and mineral dust concentrations, to within prescribed levels for humans to work in that environment. A lesser concern is the clearance of blast fumes which is normally when the mine is not occupied. In a smaller number of mine radiation and other gases, such as methane may also need consideration. A new and increasing concern as Canadian mines go deeper is the control of heat exposure to the degree that it requires more air to control the temperature of the working environment than is needed for other concerns.

Mine ventilation system is said to be homotropal when the movement of the fragmented ore is in the same direction as the fresh air, while an antitropal ventilation system is one wherein the movement of the fragmented ore is opposite to the direction of movement of fresh air. Ascentional ventilation takes the advantage of the tendency of warm air to move upwards through inclined workings and utilizing natural ventilation effects. Descentional ventilation system is employed where the air can enter the mine at a higher elevation where its cooler and drier.

BASICS

A ventilation system is basically a combination of pipes and ducts, fans, cooling and heating systems, and possibly air cleaning equipment. Air introduced into the mine workings via the pipes and ducts, and from natural openings and shafts into the mine workings flows through the workings, is affected by dust, gas, heat, or other constituents and is then removed (or exists naturally) from the workings.

Thus the information you will need to design, install, and operate a cost-effective and technically efficient ventilation system includes: surface temperatures and humidity; underground rock strata temperatures and moisture contents; rock fracture patterns to the extent they affect the air permeability of the rock; the layout of the mine workings, include options for ventilation shafts, bulkheads, and partitioning of the workings into areas for separate ventilation control; the mine operations as they will affect underground air quality including blasting and equipment emissions; the air quality standards that have to be met for human health and safety in the ventilated workings; and finally the nature and cost of energy sources to run and operate the ventilation system.

Mine ventilation system run the full spectrum of shafts and tunnels so configured that natural air drafting is sufficient to move and clean the air; to the most sophisticated modern systems where wireless sensors monitor air quality and temperatures and control systems to ventilate only specific areas when needed such as after blasting or just before the entry to the area of miners.

As noted, the system supplying air to the workings generally includes fans, ducts, and piping. Cooling and filtering equipment may also be needed. The specifics of such equipment are multiple and complex. Best you contact the manufacturers and suppliers for specific equipment facts and statistics.

A ventilation system, at is simplest, is but a pipe network through which air flows. There are many computer codes to undertake the simple, but repetitive calculations required to quantify the performance of such a system. Most computer codes incorporate the many coefficients that generally govern the flow of air in pipes, through mine tunnels, and into and out of the valves and doors that control flow. We do not repeat such flow parameters here-best buy the code and go for it.

The evaluation of a mine ventilation system can be best expresses by calculating the volumetric efficiency. It relies on the simple formula as given below:

Ventilation Efficiency (%) = 100 x Total Quantity of Air 'Usefully Employed' / Total Quantity of Air Supplied through the Main Fan(s)

GENERAL DESIGN PRINCIPLES

The following general design principles are adapted from the SME Mining Engineering Handbook's chapter on Mine Ventilation Design by Bruce Johnson and Raja Ramani (well worth obtaining and reading.)

Select main ventilation inlets and outlets.

Determine airflow requirements.

Specify fan locations.

Determine air flow resistance for all branches .

Build and run a computer model of the mine ventilation system.

Adjust system layout, design parameters, and equipment operating characteristics and rerun computer code until a viable system results.

Review the plan with operating personnel.

SOFTWARE

Here are a few of the codes you may choose to use to design, analyze, and operate you ventilation system. I include some information about the capabilities of each code, not only because this saves you looking up the links, but it also helps us understand the many aspects of a ventilation system that need be addressed.

An important feature offered by these software codes is simulation - of mine fires, gas outbursts like methane, carbon monoxide, etc.

Ventsim appears to be one of the leading computer codes for mine ventilation analysis. They describe their code thus: Ventsim is an underground mine ventilation simulation package designed to simulate airflows (and many other types of ventilation data) from a modeled network of airways. Ventsim is the first ventilation package to integrate an easy to use Windows graphical design with a 3D graphics interface.
The software is currently used by over 400 mines, universities, consultants and research organizations throughout the world; the most recent version being Ventsim Visual 2.6 (Source: Ventsim)

VnetPC: It was designed by Malcolm J Mcpherson himself as a ventilation network simulator. However, over the period of time, it has evolved with the latest one (Source: VnetPCPro). Given data that describes the geometry of the mine network, airway resistance or dimensions, and the location and characteristic curves of fans, the program will provide detailed listings and graphical representations of:

Branch Airflows.

Frictional Pressure Drops.

Airway Resistance.

Air Power Losses in Airways.

Ventilation Cost of Each Airway.

Fan Operating Points (Pressures and Airflows).

Duties of Required Regulators and Booster Fans

MineFire allows the user to simulate fires, heat flow, contaminant flow, and/or natural ventilation in underground ventilation networks using the familiar VnetPC graphical and tabular interfaces. Results are displayed both symbolically and numerically on the schematic.

DuctSIM is a simulation program designed for both the mining and tunnelling industries to assist engineers and planners with the design and modeling of fan and duct systems. It provides a new user-friendly, cost-effective tool to quickly design, model, and analyze proposed or existing duct systems ranging from small secondary fan/duct installations to large series-fan systems.According to input data, the user is able to construct models and optimize them by considering duct type and diameter, shock losses, and the number, type and spacing of fans. The program may be used for initial design, or to help troubleshoot and improve existing duct installations. It is useful in showing personnel the reasons behind a poor installation and ways to improve the system, resulting in safer working conditions.

CLIMSIM. CLIMSIM for Windows (Version 1.0) is a computer software program that is designed to aid mine ventilation and environmental engineers in the prediction of the thermodynamic and psychrometric properties of air as it flows through underground airways. The program takes into account geothermal gradient, rock thermal conductivity and diffusivity, airflow, air quality, age of the excavation, wetness of the rock surfaces and the siting and capacity of machinery, heat exchangers or other local or disseminated sources of heat and humidity.

In this superb book you will find chapters that range from the history of ventilation in mining, through the fundamentals of ventilation theory, to the physiological reactions to ventilated conditions in mines. With the resurgence of interest in uranium mining, you may be interested in the chapter of ventilation in uranium mines. This chapter takes you through the fundamentals of radioactivity, the decay of uranium to affect air quality, the impact of affected air on humans, and how to monitor and control the situation. And if you are faced with designing, updating, or managing a computer code for ventilation, you should read the chapter on the fundamental theories of ventilation and air flow in the circuits that make up a mine.

Mine Ventilation and Air Conditioning

Amazon lists over 800 books for sale on the topic of mine ventilation. One of the earliest dates from 1894 and is entitled Mine ventilation made easy: With an appendix containing detailed answers to 155 questions selected from various American examinations for mine inspectors and mine foremen. Most of the more recent volumes are proceedings of conferences.

Then there is Google.books. Undoubtedly the best read was an 1884 volume A Treatise on Practical and Theoretical Mine Ventilation by Eugene Benjamin Wilson, an "Instructor in Drifton Industrial School for Miners and Mechanics." Does anybody know the history of this school? Who can resist a book that starts:

"The author, aware of the interest manifested by miners in this subject, which is so intimately connected with their daily employment, has endeavored to deal with the subject in such a manner that no one with a fair knowledge of the English language and of arithmetic need despair of thoroughly mastering it. Knowing that the miner possesses but a comparatively small stock of words, and is not adept in algebraic formulas, the writer has taken a different position from the standard works on the subject, endeavoring to do away with obtuse language and such highly mathematical formulas as are only calculated for well-educated engineers."

COURSES

Many organizations offer courses in ventilation practice. Here are some:

The University of New South Wales in Australia offers courses on mine ventilation. Presumably this is done through the Australian National Centre for Mine Ventilation (established by the Minerals Council of Australia).

Mine refrigeration and air-conditioning: cooling options for the workplace, ranging from the impact of increased airflow, through to the full range of refrigeration solutions, including bulk air cooling on surface or underground, "spot" self-contained refrigeration plants at the workplace, and chilled service water.

Working in heat protocols and heat illness: development of appropriate working-in-heat protocols (heat management plans) designed to provide safe and healthy workplaces without necessarily introducing costly refrigeration.

Dusts and mine gases, diesel fumes and particulates: Estimates of airflows required to dilute contaminates to safe levels; ventilation design of dust or fume extraction and control systems.

Hatch describes their ventilation services thus: In order to provide acceptable environmental conditions underground, it is essential to systematically plan the ventilation, refrigeration and cooling systems on a mine. Hatch and its associates have the necessary experience and expertise to provide optimized mine cooling systems that will include the energy-efficient integration of ventilation, refrigeration, cooling distribution and pumping systems.

The Ventilation, Cooling and Refrigeration Engineering Design Group (VCREDG) offers clients a complete service package to design and install turnkey ventilation and cooling systems on mines. This extends from conceptual design to full detailed engineering and implementation. The expertise includes thermal design and optimization of ventilation systems; design and specification of refrigeration machines, process control, piping and insulation; procurement; construction management; commissioning and final acceptance of new and upgraded systems.

In Canada from Queens University we have Dr. De Souza who is a ventilation consultant for a number of mining companies and provides ventilation services to several mines in Canada. He is an Associate Professor teaching at the Department of Mining Engineering at Queen's University. He has been involved in a diversity of mine ventilation projects including ventilation audits; air quality control; solving critical ventilation problems; ventilation upgrade for existing mines; the design of ventilation raises; the design of surface intake and exhaust fan installations; analysis of the performance of main fan installations; booster fan selection and design; ventilation design for new orebodies; auxiliary ventilation design for long headings; the design of ore pass dust control systems; and ventilation surveys.

SUPPLIERS

The InfoMine suppliers database list over 70 suppliers of ventilation equipment under these categories: brattices, bulkheads, ducting, and fans. Also take a look at the categories for filters, cooling, and dust control equipment.

CURRENT PUBLICATIONS

Ventilation currently accounts for 35 to 45% of a mine's energy consumption. To minimize the amount of ventilation required in a mine, there are two basic options: change the design parameters that dictate the volume of air required, i.e., the high volumes needed for mobile diesel powered equipment through the use of clean engineers: and ensure the ventilation is being used efficiently.

They proceed to make recommendations for greater efficiency, including, redundant systems, local control, reduction of redundancy, and leak control.

Sib Mukherjee of the Indian School on Mine in Improvement of Performance of Mine Ventilation Fans, writes:

Mine ventilation fans ..run continuously for 24 hours a day, 365 days a years. Any improvement in their performance can lead to considerable savings….Generally in India variable pitch axial flow fans are used as the main mine ventilator.

He proceeds to discuss ways in which the operation of such fans may be modified in response to changing mine conditions that lead to changing air demands.

Timko and Derick of NIOSH and Twentymile Coal Company in Determining the Status of Mine Atmospheres - An Overview, write:

On a regular basis, mine personnel should obtain air samples directly form underground areas as well as remotely from sealed locations. These samples provide mine officials with data relative to the makeup of various atmospheres.

They proceed to describe gas sampling methods, and provide equations to analyze gas quality data to determine is a fire is developing or exists in the mine workings. Hence they recommend steps to deal with the fire, including ventilation options.

During the past two years, the Underground Mine Ventilation Group at PT Freeport has undertaken to upgrade their hygiene laboratory. This process has involved upgrading equipment for dust sampling and gas monitoring, as well as procurement of an OCEC analyzer for diesel particulate matter analysis. …these changes have also required reevaluation of the sampling protocols and the burden of ventilation monitoring personnel.

The paper proceeds with a detailed and fascinating examination of the laboratory, the personnel roles and responsibilities, and the contribution of the ventilation group to improving mine practice.